Earlier quoted context omitted.
> written in 0-sizes font You're... evil. I love it.
Unfortunately since it's not visible, a unscrupulous motivated candidate will just give an LVM an image of the prompt, let it OCR it, and then pass on its answer. OCRing it also defends against prompt injection with white text on a white background.
I look for motivated, careful, and vigilant candidates so if they do it and I can't tell, I am OK with it.
Most are not motivated, careful, and vigilant.
Most are careless, don't pay attention to details, and look for shortcuts.